The present invention relates to an illuminating device and a projected image display device using the same. JP-A-2002-23266 discloses an art in which an aperture is inserted in an optical path of a projection display device so as to adjust a quantity of light.
In addition, an art has been proposed in which, as a means for increasing contrast ratio of a display image of a projection display device, thereby enhancing the brightness and darkness of the display image and increasing hue depth at intermediate scale, an aperture is mechanically and rapidly inserted in the light path, with a time cycle in synchronization with an image frame, so as to dynamically adjust a quantity of light.
Alternatively, an art has been proposed in which an illuminating element is utilized so as to transmit or diffract irradiated light, thereby adjusting a quantity of light at a light emitting side.
In general, in illuminating optical systems typified by a projection display device, a high-color-rendering discharge-lamp light source, such as a metal halide lamp, a high-pressure mercury lamp, or a xenon lamp, which is high-luminance and superior in the spectral characteristics has been utilized. In addition, a light source utilizing a light emitting diode (LED), which is superior in lifetime, has recently been put into practical use.
Because high color rendering properties are demanded to the foregoing light sources, stable discharge performance and stable lighting drive performance are needed. In other words, it is required that the light source is kept lighted at a constant quantity of light and therefore, the quantity of light cannot quickly be changed.
However, in an image display device such as a front projector or a rear projection TV, in order to emphasize, in accordance with an image scene, the difference between brightness and darkness, thereby enhancing intermediate-gradation rendering power, needs to dynamically and quickly changing a quantity of light for enhancing the contrast of a projected image has been aroused.
As means for projecting an image by dynamically and quickly changing a quantity of light, arts for an illuminating device in which, as described above, an aperture is mechanically inserted in the light path, an illuminating device in which an illuminating element whose light transmission amount is changed when voltage is applied is permanently provided, and the like have been proposed.
In the foregoing mechanical illuminating device, when an aperture pivoting part is continuously and quickly pivoted forward and backward around a pivoting axis, it becomes a cause to raise mechanical vibration and acoustic noise by receiving influence of inertia of the aperture pivoting part.
Meanwhile, in the illuminating device in which the illuminating element is permanently provided in the light path of the illuminating optical system, because loss of passing light is inevitable, efficiency of light is deteriorated, whereby brightness is reduced.
In the background described above, in image display devices such as a front projector and a rear projection TV, high display-image luminance and high display-image contrast ratio are important items that raise the values of the image display devices and therefore, the mechanical illuminating device, in which, an aperture is inserted only when needed so that light for an illuminating optical system is efficiently introduced, have become dominant.
FIG. 12 is an external view of a conventional mechanical illuminating device, and FIG. 13 is a cross-sectional view of an optical apparatus equipped with the illuminating device.
In FIG. 12, reference characters 7a and 7b denote a pair of apertures for dynamically cutting off a light beam irradiated from the light source so as to narrow down the quantity of light and the apertures, each have a pivoting axis 7c, are opened or closed symmetrically with each other, through the mechanical power of an actuator 8. The illuminating device is mounted in an optical apparatus shown in FIG. 13 and incorporated in an image display device.
In general, light beams 9 emitted from a high-color-rendering point light source 1 which is high-luminance and superior in the spectral characteristics, such as a metal halide lamp, a high-pressure mercury lamp, a xenon lamp, or an LED, are condensed or parallelized, in front of the point light source 1, by a first reflector 2 utilizing an elliptic mirror or a parabolic mirror.
The apertures 7a and 7b of the illuminating device are arranged in the light path in front of the first reflector 2 and in response to an image signal of the image display device, the opening and closing operation of the apertures 7a and 7b is performed. In general, the opening and closing operation of the apertures 7a and 7b is performed, with a time cycle corresponding to every video-image frame and with high-speed direct drive way of a magnetic motor utilizing a voice coil, and the like. An optimal control signal is inputted to a servo circuit of the illuminating device to drive the actuator 8 so that the apertures 7a and 7b are pivoted in a closing direction so as to further narrow down the light beam 9 when light arrangement in an image to be displayed is dark in average, and reversely, the apertures 7a and 7b are pivoted in an opening direction to be apart from the light path so as to reduce loss in the light beam 9 when the light arrangement in an image to be displayed is bright in average.
The size of the pair of apertures 7a and 7b is required to be large enough to cover the light beam 9 emitted from the first reflector 2. When narrowing down the light beam 9, the apertures 7a and 7b are exposed to a high-intensity light beam and therefore, a material that has a high heat resistance and is hard to deform is selected. Moreover, in order to prevent interference between the frames of image projected from the projection lens, thereby dynamically narrowing down the quantity of light, the opening and closing operation of the apertures 7a and 7b is performed at high speed, with a time cycle corresponding to video image frame frequency of 60 Hz, in general; therefore, the apertures 7a and 7b are each required to have a minimal size and a minimal mass so as to ensure necessary strength thereof and reduce the inertia of the pivoting part. In order to satisfy the foregoing condition elements, a metal material such as a thin aluminum plate is suitable.
As described above, the light beam 9 that has been light-adjusted in the illuminating device passes through an integrator 12 such as, in general, a condenser lens or an illuminating rod for a kaleidoscope, so that the distribution of light intensity on the irradiation plane is improved, whereby the uniformity is raised. Subsequently, the light beam 9 passes through a spectroscope 13, such as, in general, a dichroic mirror, a prism, or a color wheel, and is converted into primary colors, such as Red, Green, and Blue, and the like. Subsequently, the resultant rays pass through a reflection-type or transmission-type image element 14, so that an image, which is a frame image in which respective primary-color images are integrated, is created, and the image passes through a projection lens unit 15 and is projected onto a screen, as a final image.
As described above, in a conventional illuminating device, by utilizing an aperture, which mechanically opens and closes, in the light path of the illuminating optical system, a light beam is dynamically narrowed down. By performing opening and closing operation with a time cycle corresponding to every image frame frequency, a projected image, in which still images each having well-defined rendering power, a high contrast ratio, and sharpness are created, is perceived as a high-quality continuous image.
However, when an artificial aperture is inserted into and removed from the light path of the illuminating optical system of a projection display device or the like, a light beam at an edge of an artifact, in other words, a light beam at a boundary portion between a dark image portion the light beam for which is cut off by the aperture and a bright image portion the light beam for which passes through the aperture without being cut off diffracts, thereby producing the difference in the light path length, whereby an aberration is caused. When the aberration exceeds a given limitation, the aberration deteriorates the image quality of an image projected onto a screen and is perceived as color unevenness.
Moreover, the aperture pivoting part continuously and rapidly repeats the forward and backward movement around the pivoting axis, and design, in which the motor torque required for acceleration and forward-and-backward switching is made to have a enough margin for the inertia of the aperture pivoting part, is needed, and therefore, the voice coil, the magnetic circuit, the servo circuit, and the like become sizable, thereby making the downsizing of the illuminating device difficult.
Still moreover, the foregoing forward and backward movement around the pivoting-axis is accompanied by a mechanical vibration and acoustic noise, and therefore, in order to improve the acoustic noise to the extent such that it can aurally be allowed, a housing of the illuminating device needs to be rigid, thereby hindering the downsizing of the illuminating device and ensuring of the reliability.